Twoterminal

Two-terminal, or twoterminal, refers to any electrical device or network that presents exactly two terminals for connection to a larger circuit. The term is used to distinguish components and networks with two external connection points from multi-terminal devices. Two-terminal constructs can be simple passive elements or complex networks composed of multiple components, as long as they have only two external terminals.

The behavior of a two-terminal device is described by its current–voltage I–V characteristic. Passive linear two-terminal devices, such as resistors, capacitors, and inductors, have predictable, time-invariant relationships and can be analyzed with linear circuit theory. Nonlinear two-terminal devices, such as diodes, exhibit nonlinear I–V curves. The energy storage elements capacitor and inductor are two-terminal devices whose response depends on time or frequency, affecting transient and AC behavior. Two-terminal networks can also include energy sources, such as batteries or solar cells, when connected in a circuit.

A fundamental tool for analyzing linear two-terminal networks is Thevenin/Norton equivalence. Any linear bilateral two-terminal network can be replaced by a Thevenin equivalent: a single voltage source in series with a resistance, or equivalently a Norton form: a current source in parallel with a resistance. These equivalents capture how the network interacts with an external circuit across its two terminals. Impedance, open-circuit voltage, and short-circuit current are common descriptors used in this context.

Applications of two-terminal analysis span circuit design, impedance matching, signal processing, and sensor interfacing. The concept underpins both practical engineering and theoretical studies, enabling simplified modeling and straightforward system-level analysis across a wide range of electrical and electronic technologies.